5.1.4 (c-d)

Question 1

What is the exocrine function of the pancreas?

Answer 1

• Most of pancreas made of glandular tissue
• The tissue is made up of acinus (group of exocrine cells)
  
  • Tissue is responsible for producing digestive enzymes (amylases, proteases, lipases) and pancreatic juice
  • The enzymes and juice are released into ductules which form the pancreatic duct carrying the contents to the duodenum (small intestine)

Question 2

What is the endocrine function of the pancreas?

Answer 2

Within the exocrine tissue there are regions of endocrine tissue called Islets of Langerhans which produce insulin and glucagon secreted directly into the blood

• α-cells – produce glucagon
• β-cells – produce insulin

Alpha cells are larger and have more cells than beta cells

Question 3

What are ways to increase blood glucose conc.?

Answer 3

• Diet: Eating carbohydrate rich foods
• Glycogenolysis: The lysis (breakdown) of glycogen to glucose, releasing the glucose into the bloodstream
• Gluconeogenesis: Production of glucose from non-carbohydrate sources. E.g. liver making glucose from glycerol (lipid) and amino acids

Question 4

What are ways to decrease blood glucose conc.?

Answer 4

• Respiration: During respiration, glucose is used to generate ATP, especially during times of strenuous activity (exercise)
• Glycogenesis: Creating glycogen from glucose (when blood glucose conc. is too high)

Question 5

What occurs in the body when blood glucose conc. becomes too high?

Answer 5

• β-cells in Islet of Langerhans detect a rise in blood glucose conc. and increase insulin secretion into the bloodstream
• All somatic cells (bar erythrocytes), have insulin receptor
  
  • Insulin binds to glycoprotein receptors, causing tertiary structure changes to glucose protein channels, allowing more glucose to enter the cell

Question 6

What does insulin do to lower blood glucose conc.?

Answer 6

• Insulin:
  
  • activates enzymes converting glucose to glycogen and fat
  • Increases respiration rate of cells – to uptake more glucose
  • Increases glycogenesis rate – insulin causes liver to absorb more glucose and do glycogenesis storing in liver and muscle cells
  • Inhibiting rate of glucagon release from α-cells

Question 7

What occurs in the body when blood glucose conc. is too low?

Answer 7

• α-cells detect a drop in blood glucose conc. and increase glucagon secretion directly into the bloodstream
• Only liver** and **fat cells have glucagon receptors
• Glucagon binds to specific membranous receptors, activating adenylyl cyclase to produce cAMP (2^nd messenger)

Question 8

How does glucagon increase blood glucose conc.?

Answer 8

• Glucagon:
  
  • Causes glycogenolysis in the liver to release stored glucose into the blood stream
  • Reduces the amount of glucose absorbed by liver cells
  • Increases gluconeogenesis (increased conversion of amino acids and glycerol into glucose in the liver)

Question 9

Describe the process of insulin secretion

Answer 9

Blood glucose concentration increases about a set level, detected by the β-cells in the Islet of Langerhans

1. At normal concentrations, the membrane potential is constant at -70mV, keeping K⁺ channels open and the sodium/potassium pump working
2. As blood glucose conc. rises, glucose diffuses into the cell
3. The glucose is metabolised by the mitochondria producing ATP
4. Increasing [ATP], ATP binds to potassium channels, closing them
   
   1. Since K⁺ can no longer diffuse out, partial depolarisation occurs (membrane potential is now -30mV)
5. Depolarisation causes V-gated Ca²⁺ channels to open, and calcium ions diffuse into β-cells
   
   1. Causing secretory vesicles containing insulin to fuse with the plasma membranes and secrete insulin